Photosensitive materials so far used in photosensitive members for electrophotography (hereinafter also referred to as "photosensitive members") include inorganic photoconductive substances, such as selenium and selenium alloys, dispersions of inorganic photoconductive substances, such as zinc oxide and cadmium sulfide, in resin binders, organic photoconductive substances, such as poly-N-vinylcarbazole and polyvinylanthracene, organic photoconductive substances, such as phthalocyanine compounds and bisazo compounds, and dispersions of such organic photoconductive substances in resin binders.
Photosensitive members are required to have the function of holding surface charges in the dark, the function of receiving light and generating charges and the function of receiving light and transporting charges. There are two kinds of photosensitive members, namely, the so-called monolayer type photosensitive member consisting of one single layer having all the three functions and the so-called laminate type photosensitive member composed of functionally distinguishable layers, namely, a layer which contributes mainly to charge generation and a layer which contributes mainly to retention of surface charges in the dark and charge transport upon receiving light. In electrophotographic image formation using these photosensitive members, the technique of Carlson, for example, is applied. Image formation by this technique includes charging of the photosensitive member by corona discharge in the dark, formation of latent electrostatic images (e.g., letters, pictures) by illumination of the charged photosensitive member surface, development of the latent electrostatic images thus formed with a toner and fixation of the developed toner images on a supporting member, such as a paper sheet. After toner image transfer, the photosensitive member is subjected to the steps of charge removal, removal of remaining toner (cleaning), residual charge neutralization by means of light (erasion), and so on, and then submitted to reuse.
In recent years, photosensitive members for electrophotography in which organic materials are used have been put to practical use because of their advantageous features such as flexibility, thermal stability and film forming property. Thus, for example, there may be mentioned photosensitive members comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluoren-9-one (described in U.S. Pat. No. 3,484,237), photosensitive members in which an organic pigment is used as the main component (described in Japanese Patent Application (OPI) No. 37543/72) (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") and photosensitive members in which a eutectic complex is used as the main component (Japanese Patent Application (OPI) No. 10735/72). A number of novel hydrazone compounds have also been put to practical use.
However, although organic materials have a number of advantageous features as compared with inorganic materials, none of organic materials can fully meet all requirements set forth with respect to the characteristic properties of photosensitive members for electrophotography. Organic materials are still unsatisfactory particularly in respect of photosensitivity and of characteristics in continuous repeated use.
Accordingly, it is an object of the invention, which has been made in view of the foregoing, to provide a photosensitive member for use in electrophotography, which has high sensitivity and shows good characteristics in repeated use, through the use, as a charge generating substance in the photosensitive layer, of a novel organic material that has not yet been used.